The objectives of this proposed study are to determine the metabolites of aflatoxin B1 formed by the very sensitive rainbow trout. Both in vivo and vitro systems will be used in this study, and the interaction between microsomal and non-microsomal metabolism will be investigated. The carcinogenicity and toxicity of identified metabolites will be assayed using either lethality to Bacillus subtilis GSY 1057, induction of hepatoma in the rainbow trout embryo, or animal feeding trials. The reduced metabolite of aflatoxin B1, aflatoxin Ro, will be fed to mice and rats to evaluate its carcinogenicity in these species. The structural requirement for toxicity and carcinogenicity will be studied as will the interaction between aflatoxin B1 and compounds with similar structures.